Brushless motor for a power tool

ABSTRACT

A Brushless Direct-Current (BLDC) motor is provided for a power tool, including a stator comprising a coil, a rotor configured to rotate with respect to the stator, terminals secured to the stator, and a sensor circuit mount attached to the stator. The sensor circuit mount defines a plane having a first side and a second side, the sensor circuit mount including Hall sensors mounted on the first side of the plane of the sensor circuit mount facing the stator. Power-supply lines are secured to the terminals to supply electric current to the coil, the power-supply lines being routed from the terminals without traversing the second side of the plane of the sensor circuit mount. The sensor circuit mount is attached to the stator by at least one fastener that extends through an opening of the sensor circuit mount and a receptacle of the stator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 16/033,585 filed Jul. 12, 2018, which is a continuation of U.S.application Ser. No. 13/704,033, filed Mar. 27, 2013 which is a nationalstage entry of PCT Application No. PCT/US2011/040306 filed Jun. 14,2011, which claims the benefit of U.S. Provisional Application No.61/354,537, filed Jun. 14, 2010, and U.S. Provisional Application No.61/354,543, filed Jun. 14, 2010. The entire disclosures of theapplications referenced above are incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

This disclosure relates to a power tool, and more particularly to anelectric brushless DC motor for a power tool and the control therefore.

BACKGROUND

The use of cordless power tools has increased dramatically in recentyears. Cordless power tools provide the ease of a power assisted toolwith the convenience of cordless operation. Conventionally, cordlesstools have been driven by Permanent Magnet (PM) brushed motors thatreceive DC power from a battery assembly or converted AC power. Themotor associated with a cordless tool has a direct impact on many of theoperating characteristics of the tool, such as output torque, timeduration of operation between charges and durability of the tool. Thetorque output relates to the capability of the power tool to operateunder greater loads without stalling. The time duration of the powertool operation is strongly affected by the energy efficiency of themotor. Since, during some operating modes cordless tools are powered bybattery modules that contain a limited amount of energy, the greater theenergy efficiency of the motor, the longer the time duration that thetool can be operated. The durability of a power tool is affected by manyfactors, including the type of motor that is used to convert electricalpower into mechanical power.

Brushed motors such as the PM brushed motors that are generally employedin power tool applications are susceptible to damaged brushes over time.The main mechanical characteristic that separates Permanent Magnetbrushless motors from Permanent Magnet brushed motors is the method ofcommutation. In a PM brushed motor, commutation is achieved mechanicallyvia a commutator and a brush system. Whereas, in a brushless DC motor,commutation is achieved electronically by controlling the flow ofcurrent to the stator windings. A brushless DC motor includes a rotorfor providing rotational energy and a stator for supplying a magneticfield that drives the rotor. Comprising the rotor is a shaft supportedby a bearing set on each end and encircled by a permanent magnet (PM)that generates a magnetic field. The stator core mounts around the rotormaintaining an air-gap at all points except for the bearing setinterface. Included in the air-gap are sets of stator windings that aretypically connected in either a three-phase wye or Delta configuration.Each of the windings is oriented such that it lies parallel to the rotorshaft. Power devices such as MOSFETs are connected in series with eachwinding to enable power to be selectively applied. When power is appliedto a winding, the resulting current in the winding generates a magneticfield that couples to the rotor. The magnetic field associated with thePM in the rotor assembly attempts to align itself with the statorgenerated magnetic field resulting in rotational movement of the rotor.A control circuit sequentially activates the individual stator coils sothat the PM attached to the rotor continuously chases the advancingmagnetic field generated by the stator windings. A set of sense magnetscoupled to the PMs in the rotor assembly are sensed by a sensor, such asa Hall Effect sensor, to identify the current position of the rotorassembly. Proper timing of the commutation sequence is maintained bymonitoring sensors mounted on the rotor shaft or detecting magneticfield peaks or nulls associated with the PM.

A brushless motor provides many advantages over conventional brushedmotors. Conventional brushed motors are substantially less durable thanbrushless motors because of the wear and tear associated with thebrushes. Also, since commutation is handled via a microcontroller,mechanical failures associated with the commutation are minimized andfail conditions are better managed and handled. Furthermore, brushedmotors are less efficient than brushless motors due to the friction andthe heat associated with the brushes and the commutator. However,brushless motors are generally more expensive than conventional brushedmotors. The most significant factors driving the cost of a brushless DCmotor are the power density, the cost of the permanent magnets andelectronic components, and complex production procedures. Challengeswith the assembly process include, for example, alignment of the variouscomponents of the motor, particularly the alignment of the PMs to thesense magnets and the Hall Effect sensor. Also, the heat generated bythe power MOSFETs presents challenges to the operation of the motor.There are also challenges in connecting the field windings as well asthe overall size and design of the brushless motor. Additionally, ashand-held power tools become increasingly smaller from an ergonomicstandpoint, it is desirable to reduce the size of the motor and thecontrol components inside the power tool.

SUMMARY

According to an embodiment of the invention, a power tool is provided.The power tool may be, for example, a drill or an impact driver,although other types of power tools may also be used. The power toolincludes a housing and a brushless DC motor housed inside the housing.The motor includes a stator and a rotor pivotably arranged inside thestator. The rotor includes a rotor shaft, a rotor lamination stackmounted on the rotor shaft to rotate therewith, and at least one magnet.A bearing is mounted on the rotor shaft to support the rotor shaft. Amount is disposed adjacent the stator along a plane perpendicular to alongitudinal axis of the rotor shaft, the mount having a bearing supportmember intersecting the longitudinal axis of the rotor shaft andarranged to support the bearing therein, the mount further supportingHall sensors axially with respect to the rotor, the Hall sensorsarranged around a circumference of the bearing support to magneticallysense the at least one magnet.

In an embodiment, a circuit board is mounted on the mount, and the Hallsensors are mounted on the circuit board. In an embodiment, the circuitboard faces the rotor. In an embodiment, the mount includes pins and thecircuit board snaps onto the circuit board via the pins.

In an embodiment, a controller is mounted on a control board, and themount includes a Hall sensor interface arranged to provide sensedsignals to a controller. In an embodiment, the control board is disposedwithin a handle portion of the power tool housing.

In an embodiment, a secondary mount is disposed adjacent the motoropposite the mount, and the secondary mount supports an end bearingmounted on the rotor shaft.

In an embodiment, the mount further includes bridge portions axiallyextending from an outer periphery of the mount to secure the mount to anouter surface of the stator.

In an embodiment, the magnet is a rotor magnet supported by the rotorlamination stack to magnetically interact with the stator. In anembodiment, the magnet extends out of the rotor lamination stack toclose proximity to the mount.

Alternatively, in an embodiment, the magnet is a sense magnet mounted onthe rotor shaft.

For a more complete understanding of the invention, its objects andadvantages, reference may be had to the following specification and tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of this disclosure in any way:

FIG. 1 depicts a perspective cross-sectional view of a power tool,according to an embodiment of this disclosure;

FIGS. 2A and 2B depict perspectives expanded views of a brushlesselectric motor, according to an embodiment of this disclosure;

FIG. 2C depicts a perspective cross-sectional view of the brushlesselectric motor of FIGS. 2A and 2B, according to an embodiment of thisdisclosure;

FIGS. 3A-3C depict various configurations for connecting stator windingsof a brushless motor;

FIG. 4 depicts an exemplary speed-torque diagram of a brushless motorwith different stator winding configurations;

FIGS. 5A and 5B depict a motor stator connected to achieve a deltaconfiguration, according to an embodiment of the invention;

FIG. 5C depicts the bus bar connection of a stator assembly, accordingto an embodiment of the invention;

FIGS. 5D-5H depict conductive plates of the bus bar of FIG. 5C and wireconnections thereto, according to an embodiment of the invention;

FIGS. 6A and 6B depict a baffle having conductive stampings to achieve adelta and a Wye configuration, respectively, according to an embodimentof the invention;

FIG. 7A depicts a prior art rotor and an accompanying sense magnet;

FIG. 7B depicts an expanded perspective view of a rotor assembly,according to an embodiment of the invention;

FIG. 7C depicts a cross-sectional view of the extended rotor magnets,according to an embodiment of the invention;

FIG. 8 depicts an exemplary conventional gear arrangement inside atransmission assembly;

FIG. 9 depicts a cross-sectional view of the motor and the control unit,according to an embodiment of the invention;

FIGS. 10A and 10B depict cross-sectional and perspective views of acontrol unit and an integrated input unit, according to an embodiment ofthe invention;

FIG. 11 depicts a perspective view of the power tool detailing the heatsink of the control unit, according to an embodiment of the invention;

FIG. 12 depicts an attachment mechanism for the heat sink, according toan embodiment of the invention;

FIG. 13 depicts a perspective view of the input unit assembly mounted onthe control circuit board, according to an embodiment of the invention;and

FIGS. 14A-14C depict views of a potting boat for potting the controlmodule, according to an embodiment of the invention.

DESCRIPTION

With reference to the FIG. 1, a power tool 100 constructed in accordancewith the teachings of the present disclosure is illustrated in alongitudinal cross-section view. The power tool 100 in the particularexample provided may be a drill/driver, but it will be appreciated thatthe teachings of this disclosure is merely exemplary and the power toolof this invention could be a circular saw, a reciprocating saw, or anysimilar portable power tool constructed in accordance with the teachingsof this disclosure. Moreover, the output of the power tool driven (atleast partly) by a transmission constructed in accordance with theteachings of this disclosure need not be in a rotary direction.

The power tool shown in FIG. 1 may include a housing assembly 102, amotor assembly 104, a control module 104, a battery pack 108, an inputunit (e.g., a variable speed trigger) 110, a transmission assembly 114,an output spindle (not shown), and a chuck (not shown) that can becoupled for rotation with the output spindle. The housing assembly 102can include a housing 102 a and a gear case 102 b that can be removablycoupled to the housing 102 a. The housing 102 a can define a housingbody and a handle 112.

According to an embodiment, the motor 104 is received in the housing 102a. The motor can be any type of motor and may be powered by anappropriate power source (electricity, pneumatic power, hydraulicpower). In the particular example provided, the motor is a brushless DCelectric motor and is powered by a battery pack 108. An input unit 110is mounted in the handle 112 below the housing 102 a. The input unit 110may be a variable speed trigger switch, although other input means suchas a touch-sensor, a capacitive-sensor, a speed dial, etc. may also beutilized. In an embodiment, variable speed trigger switch may integratethe ON/OFF, Forward/Reverse, and variable-speed functionalities into asingle unit and provide respective inputs of these functions to thecontrol unit 106. The control unit 106, which is coupled to the inputunit 110 as described further below, supplies the drive signals to themotor. In the exemplary embodiment of the invention, the control unit106 is provided in the handle 112.

The brushless motor 104 depicted in FIG. 1 is commutated electronicallyby the control unit 106. The tool 100 is powered by a suitable powersource such as the battery pack 108. It is envisioned, however, that thepresent disclosures can be applied to a power tool with an AC powersource, which may further include an AC-to-DC converter to power tomotor. Using the variable-speed input and other inputs from the inputunit 110, the control unit 106 controls the amount of power supplied tothe motor 104. In an exemplary embodiment, the control unit 106 controlsthe Pulse Width Modulation (PWM) duty cycle of the DC power supplied tothe motor 104.

Referring now to FIGS. 2A and 2B, perspectives expanded views of thebrushless electric motor 104 is depicted according to an embodiment ofthe invention. FIG. 2C depicts a cross-sectional view of the brushlessmotor 104. As shown in these figures, in an exemplary embodiment, thebrushless motor 104 includes Hall board mount assembly 210, a statorassembly 230, a rotor assembly 250, and a ring gear mount 270.

The Hall board assembly includes a Hall board mount 212 and a Hall board214. The Hall board 214 snaps onto the Hall board mount 212 via aplurality of pins 216, which may then be welded over the Hall board 214.The Hall board mount 212 includes a bearing support 218 that receives anend bearing 252 of the rotor assembly 250 (discussed below). Mounted onthe Hall board 214 are one or more Hall Effect sensors 220 arrangedaround the circumference of the bearing support 218. The Hall boardmount 212 further includes a Hall Effect Sensor interference 222 that iscoupled to the control unit 106 to provide the control unit 106 withHall Effect sense signals.

The stator assembly 230 includes a stator 240 having a plurality ofstator windings 232 housed in a stator lamination stack 242. In asix-pole three-phase brushless electric motor, as shown in thisexemplary embodiment, three stator windings 232 are provided within thelamination stack 242. Each stator winding 232 is distributed around thelamination stack 242 to form an even number of poles. In a six-polestator, each stator winding 232 includes a pair of windings arranged atopposite ends of the lamination stack 242 to face each other. The statorwindings 232 may be connected in a variety of configurations. Exemplaryconfigurations include a series delta configuration, a parallel deltaconfiguration, a series wye configuration, and a parallel wyeconfiguration. The distinguishing characteristics of theseconfigurations will be discussed later in detail. The stator assembly230 further includes a bus bar 234 coupled to the control unit 106 toreceive DC power from the control unit 106 to power the field windings232. Using the bus bar 234 and based on the input from the Hall Effectsensors 218, the control unit 106 sequentially commutates the statorwindings 232 to drive the rotor 254. In addition, the stator assembly230 includes a baffle 236 coupled to the stator 240 via snaps or pins238. The baffle 235 may include a protrusion 236 a at its low end tocontain the wiring connections from the bus bar 234 to the statorwindings 232. Alternatively, the baffle 235 may itself integrallyinclude the bus bar 234 to input power from the control unit 106.

FIGS. 3A-3C show different stator windings 232 connections used toachieve the series wye (“Y” shaped) (FIG. 3A), series delta (FIG. 3B),and parallel delta (FIG. 3C) configurations. A parallel wyeconfiguration may also be achieved, although such configuration is notexplicitly shown. The three stator windings in a six-pole brushlessmotor are typically designated as U-U₁; V-V₁; and W-W₁ windings, whereeach winding includes two poles (U and U₁, for example, designate twopoles of the same winding). The wye configuration, sometimes called astar winding, connects all of the windings to a neutral (e.g., ground)point and power is applied to the remaining end of each winding. Thedelta configuration connects the three windings to each other in atriangle-like circuit, and power is applied at each of the connections.For a given motor, the delta configuration achieves higher speed (rpm)at lower torque, whereas the wye configuration achieves relativelyhigher torque at lower speed. The parallel delta configuration achievesthe even higher speed at lower torque load. FIG. 4 depicts an exemplaryspeed-torque diagram of a brushless motor having these configurations.

In a typical off-the-shelf stator assembly for an electric brushlessmotor, the poles of each stator windings 232 (i.e., U and U₁, V and V₁,and W and W₁) are arranged opposite one another and are wound using asingle wire during the manufacturing process. Specifically, the statorhousing typically includes pre-routed wiring connections that connectsterminals 2 (U) and 7 (U₁), terminal 4 (V) and 9 (V₁), and terminals 6(W) and 11 (W₁) around or adjacent to the stator lamination stack 242(See FIG. 5A). The remaining terminals may then be wired to achieve thedesired configuration, i.e., delta or wye, in series or in parallel.

Conventionally, in a six-pole motor, three adjacent poles are designatedas U, V, and W, opposite the corresponding U₁, V₁, and W₁ poles of thesame winding 232. FIG. 5A depicts the brushless motor 104 with thisarrangement. A challenge with this arrangement, however, is thatterminals 1 (U) and 12 (W₁), terminals 5 (W) and 10 (V₁) and terminals 3(V) and 8 (U₁) must be wired together to obtain the delta configuration.It is easy to wire terminals 1 and 12 to each other, as they are locatedadjacent to one another. However, connecting terminals 5 and 10 andterminals 3 and 8 require wiring around the circumference of the stator240. Furthermore, some conventional designs utilize a printed circuitboard attached to the stator to facilitate the connections between thestator terminals, but the copper tracks of the printed circuit board aretypically insufficient in handling large amounts of current in heavyduty power tool applications, such as drills or other high torque powertools.

In order to overcome this challenge, according to an alternativeembodiment of the invention shown in FIG. 5B, the poles of the statorwindings are designated such that the terminals required for wiring adelta connection are arranged adjacent to one another. For example, inan exemplary embodiment, the designation of the stator windings poles Vand V₁ are switched such that terminals 5 and 10 as well as terminals 3and 8 fall adjacent to one another. Accordingly, the terminals can beconnected easily without the need for extra wiring through the center oraround the circumference of the stator 240. The stator windings 232 canbe comprised of one continuous coil tapped at three connection points502 a, 502 b, 502 c for connecting the stator windings 232 to the busbar 234. This arrangement significantly simplifies the motor windingprocess.

FIGS. 5C-5H depict the details of the bus bar 234 and the wiring of thestator assembly 230, according to an embodiment of the invention.

As shown in FIG. 5C, the bus bar 234 includes at least three inputterminals 502 corresponding to each of the stator windings U, V and W.In an exemplary embodiment, the input terminals 502 comprise conductiveplates 504 separated by insulating channels 506. The conductive plates504 may be made of, for example, brass material or other conductivemetal. As shown in FIG. 5D, each conductive plate 504 may include one ormore barb features 512, 514 for attaching the conductive plates 504inside the insulating channels 506. Further, as shown in FIG. 5E,conductive plates 504 may include hooks 516 for routing wires from thestator windings to the conductive plates 504. The conductive plate 504may also include hooks 518 for accommodating the wires from the controlunit 106 to the conductive plates 504.

As shown in FIG. 5F, the barb features 514 of the conductive plates 504snap into corresponding receiving slots 524 inside the insulatingchannels 506. The insulating channels 506 are shown in this figurewithout the walls separating the channels 506. Further, as shown incross-sectional view of FIG. 5G, the barb features 512 engageprotrusions 522 of the insulating channels 506 to lock the conductiveplates 504 within the insulating channels 504. Wires 530 from thecontrol unit 106 may be soldered or attached by other means inside thehooks 518. Similarly, wires 532 from the stator windings 232 may besoldered or otherwise attached inside the hooks 516. FIG. 5H depicts anexpanded view of the stator assembly 230 including the wires 532 leadingfrom the stator windings 232 and through the insulating channels 506into the hooks 516.

As discussed above, according to an exemplary embodiment, the statorwindings 232 can be connected vie wire connections arranged around thestator 240. In an alternative embodiment, according to an aspect of theinvention, the baffle 236 may include a series of metal routings stampedor adhesively connected onto the front face of the baffle 236 to connectthe desired terminals of the stator 230. The metal routings may be, forexample, made out of brass or other electrically conductive material.

FIG. 6A illustrates an example of a baffle 236 having metal stamping 602to achieve a series delta connection for the stator 240. The terminals1-12 of the baffle 236 correspond to and are electrically connected toterminals 1-12 of the stator 240. Slots 238 a on the baffle 236 areprovided to receive the snaps 238 from the stator 230. In this example,the metal stampings 602 on the baffle 236 connect terminals 1 and 12, 5and 10, and 8 and 3 to accommodate a series delta connection aspreviously described. Alternatively, as shown in FIG. 6B, the baffle 236could include metal stampings 604 connecting terminals 10, 8 and 12 toaccommodate a series wye connection.

Referring back to FIGS. 2A-2C, the rotor assembly 250 includes an endbearing 252, a rotor 254, a rotor lamination stack 256, a magnetretaining cap 258, an end cap 260, and a fan assembly 262. The rotorlamination stack 256 houses a series of permanent magnets (PMs). In anexemplary embodiment, a set of four PMs may be provided. Adjacent PMshave opposite polarities such that the four PMs have, for example, anN-S-N-S polar arrangement. The rotor 254 is securely fixed inside therotor lamination stack 256. The end bearing 252 provides longitudinalsupport for the rotor 254 in the bearing support 218 of the Hall boardmount assembly 210. As the stator windings 232 are energized anddeenergized by the control unit 106, the PMs are repelled and/orattracted to turn the rotor assembly 250 inside the stator assembly 230.The Hall Effect sensors 220 provide the control unit 106 with thesignals indicating the position of the PMs, which allows the controlunit 106 to energize the appropriate stator windings 232.

In conventional designs, as shown in FIG. 7A, sensing arrangement forbrushless motors includes a lamination stack 402 that is the same lengthas the permanent magnets 404. In addition, there is provided a separatesense magnet 406 that is coupled to the end of the lamination stack 402.The sense magnet 406 includes four poles (N-S-N-S), which must beprecisely aligned with the four permanent magnets 404 of the laminationstack 402. The sense magnet 406 is positioned relative to the HallEffect sensors (not shown) in such a way that the polarity of the sensemagnet 406, and therefore the position of the rotor, can be sensed withprecision by the Hall Effect sensors. This sense magnet 406 may or maynot have an additional back iron plate (not shown) depending on thestrength of the magnet and/or the sensitivity of the Hall Effect sensor.The sense magnet 406 may also include a mounting mechanism (plastichousing or mounting disc), which orients the alignment of the sensemagnet 406 to the permanent magnets 404. The magnetic orientation of thesense magnet 406 is axial and perpendicular to the longitudinal magneticorientation of the permanent magnets 404.

The problem arising from this arrangement is aligning the sensor magnet406 with the permanent magnets 404. There are conventional designs thateliminate the sensor magnet altogether and extend the rotor laminationstack 402 along with the rotor magnets close to the Hall Effect sensor.These designs, however, suffer from the increase in the amount of spacetaken up by the rotor lamination stack 402. In fact, some of thesedesigns extend the rotor lamination stack equally on each end in orderto align the center of the rotor lamination stack with the center of thestator. Thus, if for example the stator is 10 mm long and the permanentmagnets need to extend 3 mm to be properly sensed by the Hall Effectsensors, the entire length of the rotor lamination stack would have tobe between 13 to 16 mm.

To overcome these problems, according to an embodiment of the invention,as depicted in FIG. 7B, a rotor stack 256 is provided with permanentmagnets 282 that extend outward from the rotor lamination stack 256 onlyon one end towards the position of the Hall Effect sensors 220. The endsof these magnets 282 are used as the position sensing component for theHall Effect sensors 220. The end cap 260 is placed on the opposite endsof these magnets 282 to prevent axial movement of the magnets 282towards the fan 262. The magnet retaining cap 258 is arranged at theother end of the rotor lamination stack 236 to prevent axial movement ofthe magnets 282 towards the Hall board assembly 210 and radially capturethe extended portion of the magnets 282. Both the end cap 260 and themagnet retaining cap 258 may be made of plastic or other insulatingmaterial. The magnet retaining cap 258 includes slots 284 which tightlycapture the magnets 282. In an embodiment, the magnet retaining cap 258may be molded, snapped onto, or welded onto the rotor lamination stack256.

According to this embodiment, since the magnetic flux of the magneticorientation of the permanent magnets 282 is longitudinal, the HallEffect sensors 220 has to be optimally positioned such that they onlyintersect and sense the north or south flux of the magnet, but not both.Specifically, each of the Hall Effect sensors 220 has to be arranged atan angle α from an axis 410 of the corresponding permanent magnet 282.If the Hall Effect sensors 220 are too close to the axis 410, it mayincorrectly sense an N magnet as an S magnet or vice versa. The angle αmay vary depending on the specific motor design and the strength of theHall Effect sensors 220. This arrangement is depicted in FIG. 7C.

Referring back to FIGS. 2A-2C the fan assembly 262 is discussed herein,according to an embodiment of the invention.

Brushless motors were conventionally provided with a motor fan includinga straight fan plate that expands over the height of the motor. Fanblades extend longitudinally from the fan plate. While the presence ofthe motor fan is important for cooling the motor, the space occupied bythe blades increases the length of the motor. The fan assembly 262,according to an embodiment of the invention, minimizes the amount ofspace taken up by the fan blades. Specifically, the fan assembly 262includes a fan plate 264 and a set of fan blades 266 arranged around theedge of the fan plate 264 facing the stator 240. The back portion of thefan plate 264 faces an end cap 278 of the ring gear mount 270. The fanplate 264 is securely fastened to the rotor 254 via an encapsulationportion 268. According to an embodiment, a middle portion of the fanplate 264 is contoured as shown in FIG. 2C to accommodate a projectingportion 276 of the end cap 278 of the ring gear mount 270. This allowsthe outer portion of the fan plate 264 that supports the fan blades 266to nest inside the ring gear mount 270 adjacent the end cap 278. Thisarrangement can save the overall motor length by 1-5 millimeters. Inalternative embodiments, where a conventional ring gear mount isutilized instead of the integrated ring gear mount 270 (discussedbelow), the fan plate 264 may be contoured to nest the outer portion ofthe fan plate 264 within transmission housing above the end bearing 274.

The ring gear mount 270 is herein described by referring again to FIGS.2A-2C, according to an embodiment of the invention.

In electric power tools, the transmission assembly 114 having aplanetary gear system is typically manufactured and assembled separatelyfrom the motor assembly 104. The housing 102 of the power tool containsand holds both assemblies together. The transmission assembly 114, asshown in FIG. 8, includes a pinion (sun) gear 272, a set of at least twousually two to three) planetary gears 290, and a ring gear 292. Thepinion 272, which is attached to and rotates along with the rotor 154,engages the planetary gears 290. The planetary gears 290 in turn engagethe inside teeth of the ring gear 292. In some embodiments, theplanetary gears 290 may be attached to a planet carrier plate (notshown), which engages the ring gear 292.

Conventionally, the pinion 272 is attached to the motor rotor and ismanufactured and assembled as a part of the motor assembly. The rotor ishoused inside the motor assembly via a bearing. The ring gear 292 ishoused via a ring gear mount inside the transmission assembly. Duringthe assembly process, the center of the ring gear 292 must be alignedwith the motor rotor to fit the pinion 272 inside the transmissionassembly. This alignment is often expensive and burdensome.

To simplify this process, according to an embodiment of the invention,the ring gear mount 270 is integrated as a part of the motor assembly104. The ring gear mount 270 integrally includes the end cap 278 for themotor 104 on one side and is shaped to further include support portions294, 296 to respectively provide support for the planetary gears 290 andring gear 292 on the other side. The ring gear mount 270 alsoencapsulates the end bearing 274 via the projecting portion 276 tosupport the rotor 254. In an embodiment, the end bearing 274 and thering gear mount 270 are integrally manufactured as one piece. Thissubstantially simplifies the assembly process, as the ring gear mount270 ensures proper alignment of the planetary gears 290 and the ringgear 292 with the pinion 272.

Another aspect of the invention is discussed with referenced to FIG. 9,which illustrates the assembled view of the motor 104, and further inreference with FIGS. 2A and 2B. As shown in these figures, the statorassembly 230 is provided with receptacles 302 around the stator 240.Similarly, the Hall board mount assembly 210 and the ring gear mountassembly 270 include receptacles 304 and 306, respectively, that alignwith the receptacles 302 of the stator 240. In order to assemble thecomponents of the motor 104 together, the rotor assembly 250 is fittedinside the assembly 230, the end bearing 252 is fitted inside thebearing support 218, and the rotor 254 is fitted inside the end bearing274 of the ring gear mount assembly 270. A series of fasteners 308 passthrough the receptacles 302 and 304 from the back end of the Hall boardmount assembly and fasten into the receptacle 306 of the ring gear mountassembly 270 to complete the assembly of the motor 104.

In order to ease the alignment of the various sub-assemblies during themotor assembly process, various alignment features are providedaccording to an exemplary embodiment of the invention, as shown in FIGS.2A and 2B. These alignment features are helpful during the assemblyprocess, as they allow the sub-assemblies to be aligned with precisionprior to insertion of fasteners 308. These alignment features includepins 310 on the two sides of the stator 240 and corresponding pinreceptacles 312 on the Hall board mount assembly 210. Additionally,bridges 314 and 316 are provided on the Hall board mount assembly 210and the ring gear mount assembly 270, respectively. These bridges can beplaced fittingly between the upper and lower receptacles 312 of thestator assembly 230, as shown in FIG. 9. These alignment features helpsecure the various sub-assemblies in their desired position prior totightening the fasteners 308 to complete the assembly process of themotor 104.

The control unit 106 and the input unit 110 are discussed herein,according to an embodiment of the invention.

Referring back to FIG. 1, the control unit 106 is placed inside thehandle 102 of the tool, according to an exemplary embodiment. Thislocation provides numerous advantages over conventional locations forthe control module near the battery pack 108 or near the motor 104.Placement of the control unit 106 inside the handle 102 minimizes theinterconnections between the variable speed trigger 902/906 and theFWD/REV lever 904 of the input unit 11 and the control unit 106. Thisplacement also reduces the length of wire connections required betweenthe battery pack 108, the control unit 106, and the motor 104. Thisresults in lower cost, less complex assembly, and increased reliabilityof the system. The location of the control unit 106 also reduces theoverall length of the tool as compared to configuration where locationof control unit is behind or in the vicinity of the motor 104.

Conventionally, various components of the control unit were placed androuted together over a single Printed Circuit Board (PCB). While thisapproach may have been practical where the control unit were positionednear the motor, space limitation becomes an issue when the control unitis placed inside the handle. The ever-increasing demand for the betterergonomics, as well as the need to enable users with various hand sizesto grip the tool comfortably, has led to smaller and smaller handles ofthe tool. The aforementioned space limitation is more predominant inbrushless motor control, where the control module has a lot moreelements than a standard control. In case of brushless motor, thecontrol unit commutates the motor and controls all aspects of thebattery, input unit, and/or motor control. For example, the control unitcontrols the power to the motor, provides other control function such astwo speed selection and also provides secondary outputs such as LEDs,etc. Placing all the control unit components on a single PCB inside thehandle would substantially increase the length of the handle.

Other conventional designs utilize two separate boards for the controlcomponents and power components. The board carrying the power componentsin these designs is placed behind the motor and the board carrying thecontrol components is placed inside the handle or at the foot of thepower tool. These designs also have several disadvantages. For example,the placement of the power components behind the motor increases thelength of the power tool.

According to an embodiment of the invention, as shown in thecross-sectional view of FIG. 10A and the expanded perspective view ofFIG. 10B, in order to package the total control unit 106 inside thehandle 102, a two-board solution concept is provided. As shown in thesefigures, the control unit 102 includes a control circuit board 800arranged in parallel to a power circuit board 820. In an embodiment, thepower circuit board 820 is mounted on the control circuit board 800. Thetwo boards are interconnected via the support pins 828, 814, 804, whichalso provide various control signal and power connections between thetwo boards. This arrangement minimizes the length of the control unit106.

The control circuit board 800 includes a micro-controller 802. In anexemplary embodiment, the micro-controller 802 may be a programmablemicroprocessor, controller, or digital signal processor. The controlpins 804 are coupled to the micro-controller 802 and the power circuitboard 820. The control circuit board 800 also includes a Hall businterface 806, which is couples the micro-controller 802 to the HallEffect sensor interface 222 of the Hall board mount 212. The controlcircuit board 800 is coupled to the battery pack 108 via power inputs810. Power pins 814 provide power, as managed by the controller 802, tothe power circuit board 820. Also provided on the control circuit board800 is a bulk capacitor 812 coupled to the power inputs 810 to minimizethe effect of the parasitic inductance of the battery pack 801 powerconnections.

The bulk capacitor 812 is typically used in power tool control units forreducing the variation in voltage supplied to the power module frombattery. The capacitance and voltage requirement from the bulk capacitor812 is such that the electrolytic capacitor package size always poses achallenge for packaging. In conventional designs, the capacitor would bemounted on a separate printed circuit board with flying leads used forconnecting it to the control module. Sometimes the capacitor would bemanually soldered to the terminals of the control module. All theseconventional methods for packaging the capacitor pose issues due to leadbreakage, wire breakage from the excessive vibration.

In order to overcome this problem, according to an embodiment, the powercircuit board 820 is smaller in length than the control board 800 inorder to allow the bulk capacitor 812 and the input unit 100 to bemounted on the control circuit board 800 adjacent the power circuitboard 820. The capacitor 812 is connected to the power circuit board 820via dedicated power pins 814. By mounting the capacitor 812 on thecontrol board, the capacitor 812 can be easily accommodated inside thehandle. This also allows the capacitor to be soldered using wavesoldering just like any other through-hole components on the controlcircuit board 800.

The power circuit board 820 primarily includes a smart power module(“SPM”, also referred to as intelligent power module) 822, according toan embodiment. SPM 822 is an integrated circuit including six powerMOSFETs that power the stator windings 232 of the motor 104, as well asthe gate drivers, bootstrap circuit, and all other components needed todrive the MOSFETs. The internal circuitry of the SPM 822 is beyond thescope of this disclosure and is not discussed in detail, but would beknown to a person of ordinary skill in the art. Alternatively, it ispossible to place and rout the power MOSFETs, gate drivers, and othercircuitry directly on the power circuit board 820, according to analternative embodiment. The power circuit board 820 further includespins 828, which provide further control signal connections to thecontrol circuit board 800, and pin receptacles 828 for connecting to thecontrol pins 804 and power pins 814.

Thermal performance of the control unit 106 is an important aspect ofthe design and has conventionally been a limiting factor in theoperation of the tool. Power tool applications require significantamounts of power and thus significant amounts of current flow throughthe control and power components as well as through the motor, thusgenerating a lot of heat. Placing the control unit 106 generates asignificant amount of heat, which is particularly dissipated from thepower MOSFETs of the SPM 822, inside the handle 112. This placement isparticularly challenging since there is virtually no airflow inside thehandle 112.

According to an embodiment, in order to transfer heat efficiently awayfrom the control unit 106, a heat sink 824 is provided, as shown inFIGS. 10A, 10B and 11. According to an exemplary embodiment, the heatsink 824 includes a stamped aluminum plate attached to the SPM 822. Theheat sink 824 may include a protruded surface 842 to bypass the inputunit 110. At the end of the protruded surface 842, according to anembodiment, there is provided a tab 830 projecting inward between thecontrol unit 106 and the motor assembly 104. In one embodiment, the tab830 is provided directly underneath the fan assembly 262 to carry theheat away from the control unit 106, particularly the SMP 822, into theairflow created by the fan assembly 262. The exhaust air from the fanassembly 262 blow directly over this tab 830 at high velocity providinghigh heat transfer coefficients, since heat transfer coefficient isfunction of flow velocity.

According to a further embodiment, a second tab 840 may be provided atthe end of the protruding surface 842. The second tab 840 is bent nearthe forward/reverse switch 905 of the input unit 110. The gap around theforward/reverse switch 905, as well as the gap around the variable speedtrigger switch 902, provides further airflow to transfer heat away fromthe tab 840. In a further embodiment, in order to increase the surfacearea of the tabs 830 and/or 840 and, consequently, improve the thermaltransferability of the heat sink 824, a series of V-shaped grooves 832are provided over the surfaces of the tabs 830 and/or 840.

In order to decrease the overall length of the power circuit board 820,through-holes 850 for attachment of the heat sink 824 to the powercircuit board 820 are provided directly on the SPM 822. This arrangementis depicted in FIG. 12. This arrangement is different from theconventional attachment mechanism, which required through-holes (denotedby reference 852) to be provided on the control circuit board 820outside the area of the SPM 822. This arrangement allows reduced lengthof the power board 820.

Additional ways to improve thermal performance of the heat sink,according to an embodiment, includes providing air vents at the bottomof the handle 112 of the tool to improve air flow over the heat sink 824and reduce the temperature rise. Furthermore, a series of fins can beprovided on the heat sink base to further improve heat transfer from theheat sink. Advantages of the thermal system described herein includehigher heat transfer by achieving higher heat transfer coefficients andhigher heat transfer flux per unit weight, thus providing a lightersystem. Additionally, the above-described embodiments provide lowertemperature for the power electronics components, resulting in betterswitching performance and increased reliability of the tool.

Another aspect of the invention is discussed herein with reference toFIG. 13.

In conventional power tool applications, the input unit assembly (i.e.,variable-speed switch assembly) is provided as a stand-alone unit andattached via wire connections to the control module. This isparticularly due to the fact that most power tool manufacturers in theindustry purchase switch assemblies from outside suppliers. This designrequires wiring through the handle and/or other tool components. Thismakes the assembly complicated as well as reduces the reliability ofsystem due to the possibility of failure in the interconnection.

As shown in this figure, according to an exemplary embodiment, the inputunit 110, in this case a variable-speed switch assembly, is mounteddirectly on and integrated with the control circuit board 800. Accordingto an embodiment, the variable-speed switch assembly 110 includes atrigger 902 connected to a variable-speed plunger 906. In an exemplaryembodiment, the variable-speed plunger 906 is in turn coupled to apotentiometer, although other variable-speed sensing mechanism may alsobe utilized. The potentiometer is linearly actuated, meaning that as theuser pulls the trigger, the potentiometer output varies linearly as thetrigger is pulled. In an exemplary embodiment, the plunger 906 isconnected to a wiper that slides over a series of resistive plates,which vary the output voltage of the variable-speed switch assembly 110based on the position of the wiper. Furthermore, the variable-speedswitch assembly 110 includes a forward/reverse lever 904 coupled to aforward/reverse switch 905 (FIG. 11). The variable-speed switch assembly110 provides the micro-controller 802 with an on/off signal upon theactuation of the trigger 902. The variable-speed switch assembly 110also provides the micro-controller 802 with forward/reverse signalsbased on the position of the forward/reverse lever 904, and avariable-speed voltage from the potentiometer. The micro-controller 802controls the duty cycle of the motor 104 according to these inputs. Asshown in FIG. 13, since the variable-speed switch assembly 110 ismounted directly on the control circuit board 800, these inputs can beprovided via pins 910 without using additional wiring. Tracks on thecontrol circuit board 800 directly carry these signals from the pins 910to the micro-controller 802. Furthermore, snaps 908 are provided forsecuring the variable-speed switch assembly 110 over the control circuitboard 800. This arrangement provides the several advantages in reducingwire ups, reducing the number of components, and increasing reliabilityof the device.

A further aspect of the invention is in connection with formation of alabyrinth 924 between a potting boat 922 and the input unit 110 to forma dam for the potting process, according to an exemplary embodiment withreference to FIGS. 14A-14C.

Power tools are subjected to a lot of vibrations. Designing controlmodules exposed to excessive vibrations is particularly challenging ascontrol modules have a lot of solder joints which could break, crack,become intermittent, or even open when there is relative motion betweenthe two components soldered. Failure of even a single solder joint mightresult in complete control module to become non functional.

In addition, power tools often operate in harsh environment which hasfine dust, metal dust etc. Thus, power tools are subjected to a lot ofcontamination. Contamination could short two opposite polarityconnections on the board and ultimately result in non-functional board.

In order to avoid damage to the control modules from vibration andcontamination, the control modules are often potted. The pottingcompound is typically epoxy-based compound that is cured. When cured,the control module becomes a brick like structure capable to withstandvibration and contamination. FIG. 14A depicts a potted control unitincluding the potting boat 922 and potting compound 920 surrounding thecontrol unit 106, according to an embodiment. The potting boat 922 maybe made up plastic or similar material.

The potting process includes two steps: potting the bottom side of thecontrol circuit board 800, placing the control unit 106 (including thecontrol circuit board 800) inside the potting boat 922, and laterpotting the remainder of the potting boat 922. Alternatively, thepotting boat 922 may be pre-filled with the potting compound 920 andthen the control module 106 may be pushed into the potting boat 922. Theboards 800, 820 may include holes for the pre-filled potting compound920 to escape through as the control module 106 is lowered into thepotting board 922. FIG. 14B shows the potting compound within thepotting boat 922, according to an embodiment.

As described above, the input assembly 110 is mounted directly on thecontrol circuit board 800. This requires a portion of the potting boat922 to be cut out to accommodate the input unit 110. This arrangementcomplicates the potting process, as the potting compound 920 will simplyleak out through the cut-out portion of the potting board. The cut-outportion 928 corresponding to the input unit 110 is depicted in FIG. 14C.

To prevent the potting compound 920 from pouring out of the potting boat922 during the potting process, a labyrinth design including a tongue926 (FIG. 13) on the input unit 110 and a groove 924 (FIG. 14C) on thepotting boat 922 is employed to trap the potting compound 922. Thegroove 924 is provided at the cutout portion 928 of the potting boat922. When the input unit 110 is mounted on the control unit 106, thetongue 926 and the groove 924 form a labyrinth, which traps the pottingcompound 920 inside the potting boat 922 and prevents it from pouringout of the potting boat 922. In addition, the labyrinth avoids forcesfrom impact and vibration from being transferred directly to the inputunit 110.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the scope of the invention.

The invention claimed is:
 1. A power tool comprising: a housing; a Brushless Direct-Current (BLDC) motor housed inside the housing, the motor comprising: a stator comprising a coil; a rotor configured to rotate with respect to the stator, the rotor being mounted on a rotor shaft; a sensor circuit mount member attached to the stator, the sensor circuit mount member defining a plane having a first side and a second side, the sensor circuit mount member including a bearing support formed on the first side of the plane facing the rotor that receives a bearing of the rotor shaft, wherein the circuit board mount member is secured to the stator to support the rotor bearing relative to the stator; a circuit board mounted on the sensor circuit mount member on the first side of the plane facing the rotor; a plurality of Hall sensors mounted on the circuit board around the bearing support facing the rotor; a secondary mount member disposed adjacent the motor opposite the sensor circuit mount member, the secondary mount member supporting an end bearing mounted on the rotor shaft; a plurality of terminals secured to the stator; and a plurality of power-supply lines secured to the plurality of terminals to supply electric current to the coil, the plurality of power-supply lines being routed from the plurality of terminals without traversing the second side of the plane of the sensor circuit mount member, wherein the secondary mount member comprises a receptacle that securely receives a fastener therein, the fastener being received through an opening of the sensor circuit mount member and a corresponding receptacle on the stator.
 2. The power tool of claim 1, wherein the sensor circuit mount member is attached to the stator by a fastener that extends through an opening of the sensor circuit mount member.
 3. The power tool of claim 1, wherein the circuit board includes a center through-hole around which the plurality of Hall sensors is mounted, wherein the rotor bearing is received through the center through-hole into the bearing support of the sensor circuit mount member.
 4. The power tool of claim 1, wherein the sensor circuit mount member comprises a plurality of pins and the circuit board snaps onto the sensor circuit mount member via the plurality of pins.
 5. The power tool of claim 1, further comprising a controller mounted on a control board and a Hall sensor interface mounted on the circuit board to provide sensed signals to the controller.
 6. The power tool of claim 5, wherein the control board is disposed within a handle portion of the housing.
 7. The power tool of claim 1, wherein the sensor circuit mount member further comprises a plurality of bridge portions axially extending from an outer periphery of the sensor circuit mount member to secure the sensor circuit mount member to an outer surface of the stator.
 8. The power tool of claim 1, the plurality of terminals is arranged on an outer circumference of the stator.
 9. The power tool of claim 1, wherein the stator comprises a plurality of axial recesses on an outer circumference thereof.
 10. A Brushless Direct-Current (BLDC) motor comprising: a stator comprising a coil; a rotor configured to rotate with respect to the stator, the rotor being mounted on a rotor shaft; a sensor circuit mount member attached to the stator, the sensor circuit mount member defining a plane having a first side and a second side, the sensor circuit mount member including a bearing support formed on the first side of the plane facing the rotor that receives a bearing of the rotor shaft, wherein the circuit board mount member is secured to the stator to support the rotor bearing relative to the stator; a circuit board mounted on the sensor circuit mount member on the first side of the plane facing the rotor; a plurality of Hall sensors mounted on the circuit board around the bearing support facing the rotor; a plurality of terminals secured to the stator; and a plurality of power-supply lines secured to the plurality of terminals to supply electric current to the coil, the plurality of power-supply lines being routed from the plurality of terminals without traversing the second side of the plane of the sensor circuit mount member, wherein the sensor circuit mount member further comprises a plurality of bridge portions axially extending from an outer periphery of the sensor circuit mount member to secure the sensor circuit mount member to an outer surface of the stator.
 11. The BLDC motor of claim 10, wherein the sensor circuit mount member is attached to the stator by a fastener that extends through an opening of the sensor circuit mount member.
 12. The BLDC motor of claim 10, wherein the circuit board includes a center through-hole around which the plurality of Hall sensors is mounted, wherein the rotor bearing is received through the center through-hole into the bearing support of the sensor circuit mount member.
 13. The BLDC motor of claim 10, wherein the sensor circuit mount member comprises a plurality of pins and the circuit board snaps onto the sensor circuit mount member via the plurality of pins.
 14. The BLDC motor of claim 10, further comprising a secondary mount member disposed adjacent the motor opposite the sensor circuit mount member, the secondary mount member supporting an end bearing mounted on the rotor shaft.
 15. The BLDC motor of claim 14, wherein the secondary mount member comprises a receptacle that securely receives a fastener therein, the fastener being received through an opening of the sensor circuit mount member and a corresponding receptacle on the stator.
 16. The BLDC motor of claim 10, the plurality of terminals is arranged on an outer circumference of the stator.
 17. The BLDC motor of claim 10, wherein the stator comprises a plurality of axial recesses on an outer circumference thereof.
 18. A power tool comprising: a housing; a Brushless Direct-Current (BLDC) motor housed inside the housing, the motor comprising: a stator comprising a coil; a rotor configured to rotate with respect to the stator, the rotor being mounted on a rotor shaft; a sensor circuit mount member attached to the stator, the sensor circuit mount member defining a plane having a first side and a second side, the sensor circuit mount member including a bearing support member formed on the first side of the plane facing the rotor that receives a bearing of the rotor shaft, wherein the circuit board mount member is secured to the stator to support the rotor bearing relative to the stator; a circuit board mounted on the sensor circuit mount member on the first side of the plane facing the rotor; a plurality of Hall sensors mounted on the circuit board around the bearing support member facing the rotor; a plurality of terminals secured to the stator; and a plurality of power-supply lines secured to the plurality of terminals to supply electric current to the coil, the plurality of power-supply lines being routed from the plurality of terminals without traversing the second side of the plane of the sensor circuit mount member, wherein the sensor circuit mount member further comprises a plurality of bridge portions axially extending from an outer periphery of the sensor circuit mount member to secure the sensor circuit mount member to an outer surface of the stator. 